Blow molding apparatus

ABSTRACT

A blow molding machine having a mold cavity, a blow needle bore opening into the cavity with a blow needle in the bore, a vacuum source for drawing blow air from a molded article and an exhaust passage extending from the blow needle bore to the source for reducing pressure within the blown article.

FIELD OF THE INVENTION

The field of the invention is blow molding sealed aseptic bottles,methods for blow molding sealed aseptic bottles and apparatus for blowmolding such bottles.

The sealed bottles are manufactured and may be stored for a periodbefore being filled and resealed, conventionally by applying a cap orother closure, without destroying sterility. There is no need tosterilize the bottles before filling. The bottles may be filled withfood products such as milk, juices and the like, medical fluids such assaline solution and blood, or any other contents requiring a sterilecontainer.

DESCRIPTION OF THE PRIOR ART

Conventional aseptic bottles are blow molded from parisons using sterileair, vented and then sealed in the mold halves at atmospheric pressure.

It is also conventional to blow mold bottles, fill the freshly moldedbottles while in the mold and then seal the filled bottles to assure thesterility of the bottle and contents.

SUMMARY OF THE INVENTION

The invention relates to a blow molded sealed aseptic bottle havingwalls susceptible to deformation after molding. The bottle ismanufactured from a parison using a continuous or rotary blow moldingprocess operating at a rapid rate with a very short residence time inthe mold.

Deformation of the bottle is prevented by blow molding the parisonconfined in a mold cavity using high pressure sterile blow air,maintaining the pressure of the blow air in the bottle in the mold for asufficient time to cool and set the outer or skin plastic in contactwith the mold, venting the blow air out of the bottle so that theresidual air in the bottle is expansion-cooled, reducing the pressure ofthe cooled residual blow air in the bottle below atmospheric pressureand then sealing the bottle at subatmospheric pressure. After sealingthe mold opens, the bottle is ejected and the residual heat in theplastic slowly dissipates as the plastic cools to ambient temperatureand stabilizes. The residual heat warms the cool negative pressure airsealed in the bottle to increase the interior pressure to atmosphericpressure or very near atmospheric pressure and prevent pressuredifferentials across the walls of the bottle sufficient to deform thebottle during stabilization.

The molds used for molding and cooling the aseptic bottles aresufficiently cooled to maintain a low temperature capable of rapidlycooling and setting the skin plastic in the bottle while the bottle isin the mold. This rapid cooling capability together with the reductionof the pressure of the expansion cooled residual blow air sealed in thebottle permits extremely rapid and efficient manufacture of the asepticbottles with minimum residence in the mold after blowing. For instance,aseptic bottles may be manufactured on a vertical rotary blow moldingmachine carrying a total of 14 circumferentially spaced molds androtating at a rate of approximately 6.5 revolutions per minute. Themachine produces aseptic bottles at a very high production rate of about91 bottles per minute.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings illustrating the invention, of which there arethree sheets and one embodiment.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are cross sectional views taken through a pair of moldhalves illustrating blow molding of a parison to make a sealed asepticbottle;

FIG. 3 is an enlarged view of a portion of FIG. 3 showing the sealclosing the molded bottle;

FIG. 4 is a perspective view of the molded, sealed and deflashed bottle;and

FIGS. 5 and 6 are sectional views of the bottle taken along lines 5--5and 6--6 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Sealed aseptic plastic bottle 10 is blow molded from an extruded moltenparison 12 using a pair of complementary mold halves 14 and 16 as shownin FIGS. 1 and 2. The bottle 10 is made from high density polyethyleneresin extruded in parison 12, although other resins, or even coextrudedresins, may be used as desired.

The mold halves include bottle recesses 18, blow dome recesses 20 andshallow seal neck recesses 22 connecting recesses 18 and 20. When themolds are closed as in FIG. 2, the recesses form joined blow dome, sealneck and bottle cavities. The diameter of the extruded parison 12 may begreater than the diameter of the parison illustrated and may be greaterthan the widths of the recesses at the top of the mold. When extruded,the high density polyethylene parison 12 has a high temperature in therange of about 400 to 450 degrees F.

Mold half 16 carries a blow needle 24 which may be extended into theblow dome cavity. The needle is connected to a source of sterile blowair 25 through an appropriate valving system. A drive moves the needleback and forth between a retracted position shown in FIG. 1 and anextended position in which the needle tip is located within the blowcavity dome. Each mold half 14, 16 carries a sealing blade 26, 28movable into the seal neck cavity 22 by drive means, not illustrated,for closing the seal neck of the blown bottle as shown in FIG. 3. Moldhalves 14 and 16 are provided with water cooling manifolds (notillustrated). Water at a temperature of about 40 to 50 degrees F.circulates through the manifolds and maintains the mold halves at a cooltemperature.

Needle 24 is fitted in bore 27 in mold half 16 as illustrated. Exhaustpassage 50 intersects the bore a short distance outwardly from theadjacent blow dome recess 20. When retracted, the tip of the needle 24is withdrawn past the passage 50 so that pressurized blow air is venteddirectly out to the needle bore 27 and passage 50. During venting, theneedle valving system is closed to prevent vent air from flowing throughthe needle.

Passage 50 is connected to the low pressure port of high flow rate, lowpressure venturi 52. Exhaust line 54 is connected to the venturi exhaustport and is vented to atmosphere. Line 56 connects the venturi inletport to pressurized air source 58 through valve 60. See FIGS. 1 and 2.Valve 60 is opened to flow pressurized air through the venturi at a highflow rate and out the exhaust line to atmosphere. The low pressure portand main passages in the venturi have a relatively large cross sectionalareas and do not restrict the exhaust flow of blow air through bore 27and passage 50. The venturi rapidly reduces the pressure in the mold toabout negative 2 psi.

Plastic bottle 10 includes a generally square body 30 having four thinflat sidewalls 32 extending between bottom 34 and a thin shoulderportion 36. The bottle may be made of high density polyethylene or othersuitable resins or combination of resins. The shoulder portion extendsupwardly from the sidewalls 32 to a thin annular bead 38 and thincylindrical bottle neck 40 at the top of the bottle. The neck may beprovided with threads or other closure structure engageable with a capor other closure to seal the bottle when opened and filled. A welded,redundant seal 42 extends between bottle top 40 and blow dome 44. Blowneedle opening 46 extends through the side of the blow dome.

The thin bottle sidewalls are about 0.016 inch thick and are about 6inches high and 4 inches wide. The flat sidewalls may include 1/8 inchhorizontal corrugations (not illustrated) conforming to horizontalcorrugations in the mold halves (not illustrated). Bottom 34 isrelatively thick having a thickness of approximately 0.030 to 0.040 inchor a greater thickness, depending upon the requirements of theparticular bottle. Thick flash 45 is attached to the bottle whichejected from mold halves 14 and 16. The flash has been partially trimmedaway in FIGS. 4-6.

The parison is extruded at a high temperature of about 400° to 450°degrees F. with the plastic resin in an easily flowable, molten or nearmolten state. During manufacture of the bottle the plastic in theparison cools from the extrusion temperature down through a settemperature of about 120° to 140° degrees F. and ultimately to ambienttemperature. When cooled to the set temperature the plastic becomes hardand is no longer soft and flowable. The molecular structure of thehardened, set plastic stabilizes as it cools down from the settemperature to ambient temperature. During stabilization physicaldeformation of the bottle from the molded shape can be permanentlylocked into the fully stable plastic resulting in a deformed and rejectbottle. During stabilization the plastic thermally contracts, stressrelaxes and crystallizes.

The plastic used in manufacturing bottles is a very good insulator andtakes a long time to fully cool to ambient temperature. At the time thebottle is ejected from the cooled mold the outer plastic skin has beencooled below the set temperature and is hard. The plastic locatedinwardly of the skin is hotter than the skin plastic and in thick bottom34 is above set temperature and soft. In order to fully cool the bottleit is necessary to remove all the residual heat in the plastic aboveambient temperature.

Initial cooling and removal of the residual heat from the plastic in theejected bottle occurs relatively rapidly with about 85 to 90 percent ofthe residual heat removed from the plastic during the first hour afterejection. A total of approximately 48 hours of cooling is required toremove all residual heat from the plastic so that all of the plastic inthe bottle is at ambient temperature and fully stabilized. A longer timeis required to remove residual heat from the thick bottom of the bottlethan is required to remove the residual heat from the thinwall sectionsof the bottle.

Stabilization occurs during cooling of the plastic in the sealed bottlebelow the set temperature. In order to assure that the shape of thebottle, when fully cooled, conforms to the molded shape it is necessaryto prevent physical deformation of the hard, plastic during the entirecooling cycle. Deformation such as ballooning or flexing of the flatsidewalls (with or without corrugations) occurs when the temperature ofthe air sealed in the bottle is increased by release of residual heatfrom the plastic. The heated air expands, increases internal pressureand balloons the walls of the bottle outwardly. Subsequent stabilizationof the plastic in the ballooned sidewalls locks in the deformed shapeand ruins the bottle. The bottle must be sealed to maintain sterility.It is not possible to equalize pressure by puncturing or opening thebottle during cooling.

The shape of the molded, sealed aseptic bottle is maintained throughfull cooling to ambient by reducing the pressure of the cool air in thebottle below atmospheric pressure when the bottle is sealed. Residualheat in the plastic in the ejected bottle warms and expands the cooled,subatmospheric air in the interior of the bottle to maintain an interiorpressure sufficiently equal to outside atmospheric pressure to preventbulging or ballooning of the bottle during cooling. In bottle 10, it isnecessary to maintain the interior bottle pressure to within about 1/2pound per square inch of atmospheric pressure in order to preventpressure ballooning of the thin, flat corrugated bottle sidewalls.

The plastic in the bottle shrinks during cooling and as a result theinterior volume of the bottle decreases during the first 5 to 10 hoursof cooling. The decrease in volume increases interior pressure and therisk of ballooning. The negative atmospheric pressure of the air in thebottle, when sealed in the mold, is adjusted to compensate for thefuture decrease in volume and consequent increase in pressure because ofbottle shrinkage. Unless compensated for, shrinkage alone can outwardlyballoon thin bottle sidewalls with the result that these walls stabilizein the ballooned, deformed shape and ruin the bottle.

The step-by-step molding of bottle 10 will now be described.

The hot, sterile parison 12 is extruded between the open mold halves asshown in FIG. 1. The mold halves are closed thereby capturing a portionof the parison within the bottle, seal neck and blow dome cavities. Uponclosing of the mold halves the edges of the recesses intersect theparison and form flash 45 integral with the captured parison outside ofthe mold cavities. The flash at the top and bottom of the bottle isshown in FIG. 2.

After the mold halves are closed the retracted blow pin 24 is extendedinto the blow dome cavity formed by recesses 20 and punctures the hollowconfined hot parison. Sterile blow air at a pressure of approximately 80lbs. per square inch is flowed through the needle and into the parisonto inflate the parison against the blow dome, seal neck and bottlecavities to form a body having a single interior volume filled withpressurized, sterile blow air. The blow air holds the plastic inintimate contact with the walls of the mold halves to cool the plastic.The entire outer surface or skin of the bottle is cooled below the settemperature and hardens. Some skin portions may be cooled below ambienttemperature. The plastic inside the skin is hotter than the skin. Theinner plastic in the thinwall portions of the bottle may be set. Theinner plastic in the thick bottom remains at a temperature above the settemperature and is soft.

During cooling of the bottle plastic in the mold the blow air is heatedto about 200° to 250° degrees F. Following cooling and setting of thebottle skin the blow needle 24 is withdrawn to allow the confinedpressurized and hot blow air to vent quickly to atmosphere throughrelatively large cross section bore 27, exhaust passage 50, the lowrestriction passages of venturi 52 and exhaust line 54. At the same timevalve 60 is opened and a large volume of pressurized air flows throughthe venturi 52. The air may be at an initial pressure of about 80 psi.This flow does not restrict venting of the pressurized blow air. Therapid flow of pressurized blow air out of the bottle interior 48 reducesthe pressure in the interior of the bottle thereby expanding and coolingthe remaining blow air in the bottle to a low temperature believed to bebelow ambient temperature.

Venting of the pressurized blow air in bottle 48 reduces the pressure inthe bottle interior to atmospheric pressure. Immediately after thepressure in the bottle interior 48 falls to atmospheric pressure venturi52 quickly draws air from interior 48 through lines 27 and 50, into theventuri and out line 54 to atmosphere, reducing the pressure in thebottle interior below atmospheric pressure. The venturi rapidly reducesthe pressure in bottle interior 48 to a pressure of about negative 2psi.

The venturi permits free pressure venting of the blow air andimmediately further reduces the pressure of the bottle when the pressureof the remaining air has been reduced to atmospheric pressure. Itsoperation is automatic and does not require sophisticated controls,sensors or valves. If desired, the amount of pressure reduction can bevaried by varying the pressure of the air supplied to the venturi fromsource 58.

With the interior of the bottle at the desired negative pressure thedrivers for sealing blades 26 and 28 are actuated to extend the bladesinto the neck seal cavity formed by surfaces 22 thereby engaging theopposite sides of the confined hollow plastic in the recess and forcingthe respective sides across the cavity and into welding engagement withthe opposite sides to join the plastic together and form a seal 42closing the sterile, negative pressure bottle interior 48. At the sametime the valve 60 is closed to cut off the flow of air through theventuri.

The driving forces required for moving blades 26 and 28 and forming thedesired seals is relatively high. Mold halves 14 and 16 may carryinsulating inserts at recesses 22 in order to prevent the plastic in theseal neck cavity from being cooled below a welding temperature.Preferably, extension of the blades 26 and 28 not only welds togetherthe layers of plastic captured between the blade ends and the walls ofrecesses 22 but also welds together the plastic layers extendingdiagonally between the tip ends of the two blades to form an effectivetriple redundant seal closing off bottle interior 48. The interior ofsealed bottle 10 is sterile. This is assured by the high temperature ofthe parison when extruded and captured by the mold halves and the use ofsterile blow air.

After cooling and setting of the skin of the sealed aseptic bottle, themold halves 14 and 16 are opened and the bottle is ejected from the blowmolding machine. At the time the bottle is ejected, the inside of thethick bottom 34 has cooled but is still above the set temperature and issoft and pressure deformable. The temperature of the inside of thebottom is about 180 to 200 degrees F. The skin of the bottle has beencooled to about 60 degrees F, nearly the mold temperature. In order tomaximize production, the mold opens and the bottle is ejected as soon asthe bottle skin hardens and the bottle is rigid. When ejected, thesubatmospheric pressure in the bottle bows the thin sidewalls inwardly.These walls quickly return to the molded flat shape as the confined airwarms.

As the ejected bottle cools to ambient temperature and residual heat inthe plastic is given off, the outer plastic, including the skin warms,the hot inner plastic cools and the cool air in the bottle warms andexpands, increasing and maintaining the pressure in the bottle tosubstantially atmospheric pressure. The inner bottom plastic sets.Maintenance of substantial atmospheric pressure within the bottle, plusor minus about 1/2 psi prevents ballooning of the bottle. The bottlewalls, including flat and easily ballooned sidewalls 32, do not bulge. Agreater pressure differential across the wall of the bottle is capableof ballooning the bottle during stabilization of the plastic withresultant permanent deformation of the bottle as previously described.

The shape of the final cooled bottle depends upon the temperature of theatmosphere surrounding the bottle as the plastic slowly cools afterejection from the mold halves. The negative pressure in the bottle whensealed is adjusted to assure proper geometry, without ballooning thesidewalls, when the bottle cools in an environment having apredetermined ambient temperature, say 70 degrees F. If the bottle iscooled in a higher temperature environment, say 100 degree F., then thepressure in the interior would be increased by approximately 4 percentand the sidewalls would balloon. Ballooning of the sidewalls before fullstabilization sets the sidewalls in a permanent and unacceptableballooned shape. The bottle will not return to the desired flat sidewallshape when opened. This problem can be avoided by cooling the bottles ina controlled temperature environment.

While we have illustrated and described a preferred embodiment of ourinvention, it is understood that this is capable of modification, and wetherefore do not wish to be limited to the precise details set forth,but desire to avail ourselves of such changes and alterations as fallwithin the purview of the following claims.

What we claim as our invention is:
 1. An apparatus for sealing blowmolded plastic bottles at subatmospheric pressure including:a. a moldhaving a pair of mold halves each including a body recess, a blow domerecess and a shallow seal neck recess, the seal neck recess beinglocated between and connecting the body recess and the blow dome recess,said recesses being formed in opposing faces of the mold halves acrossfrom each other respectively so that when the mold halves are closed therecesses define hollow and joined blow dome, seal neck and body cavitieswith the seal neck cavity being located between the body and the blowdome cavities, the cavities forming a single interior volume when themold is closed; b. a blow needle bore in one mold half, the bore openinginto a said blow dome recess; c. a hollow blow needle in the bore, theneedle having a tip, and needle drive means for moving the needle alongthe bore between an extended position in which the tip of the needle islocated within the blow dome cavity when the mold is closed and aretracted position in which the tip of the needle is located in the borea first distance away from the wall of the adjacent blow dome recess; d.a blow air exhaust passage partially in said one mold half, the passagehaving a first end joining the blow needle bore a distance from the wallof the adjacent blow dome recess less than said first distance and asecond end; e. a venturi having a low pressure port and a passage, saidsecond end of the blow air exhaust passage being connected to the lowpressure port; the pressure drop at the low pressure port beingsufficient to reduce the pressure in a plastic body blown in theinterior volume of the closed mold below atmospheric pressure withoutrestricting free exhaust flow of blow air out of the plastic bodythrough the needle bore and the blow air exhaust passage; f. a firstsource of pressurized air connected to the main passage of the venturiwhereby pressurized air flowing through the main passage reduces thepressure in the interior volume defined by the closed mold halves; g. asecond source of pressurized air connected to the end of the blow needleaway from the tip of the needle, and a valve connecting the secondsource of pressurized air to the needle; h. a sealing blade bore in oneof the mold halves, one end of said blade bore opening into the sealneck recess in said mold half; and i. a sealing blade in said bladebore, said blade having a sealing end, and sealing blade drive means formoving the blade along said blade bore between an extended position inwhich the sealing end of the blade is located adjacent the surface ofthe seal neck recess in the other mold half to form a seal in theplastic in the seal neck to close the plastic body in the body cavity ata negative pressure, and a retracted position within said blade bore. 2.Apparatus as in claim 1 wherein the pressure air of said second sourceof pressurized air is sterile and the sealed interior of a plastic bodyblown in the interior volume of the closed mold is sterile.
 3. Apparatusas in claim 2 wherein said venturi reduces the pressure within a plasticbody blown in the interior volume of the closed mold to about -2 poundsper square inch.